1. Field of the Invention
The present invention relates to a video signal processing method and apparatus in which a high definition (HD) video signal is processed after being divided into a signal which is suitable for reproduction as a standard definition (SD) video signal and a signal from which a HD image can be reproduced by processing it together with the SD video signal. Particularly, the present invention relates to a video signal processing method and apparatus suitable for deriving a video signal corresponding to an SD signal from a HD signal.
2. Description of the Prior Art
The television broadcasting of HD image signals such as High-Vision is becoming more popular. The television broadcasting of SD image signals such as in the NTSC system is so widely used that such systems should continue for the forseeable future. In view of this, it is convenient that video devices such as a video tape recorder (VTR) is capable of handling images of both the HD video signal and the SD video signal. An image signal processing system has been proposed which is compatible with both the HD image signal and the SD image signal. In such proposal, a portion of a bit stream which is obtained by coding an image information of the HD signal is derived and decoded to obtain an image information of the SD image signal.
FIG. 1 shows the basic construction of a known recording and reproducing apparatus which is capable of recording and reproducing both the SD image signal and the HD image signal. In FIG. 1, an HD signal Ghd is supplied to an encoder 10 in which an SD image signal Gsdh is derived from the HD image signal Ghd. The SD image signal Gsdh is supplied from one output of encoder 10 through a switch 12 to a recording and reproducing apparatus 14. The remaining additional image signal Ghdr appears at a second output of encoder 10 and is also applied to the recording and reproducing apparatus 14. When the SD image signal Gsd, also applied directly to switch 12, is to be recorded, the Gsd signal is supplied to the recording and reproducing apparatus 14 by switching the switch 12. In this case, the additional image signal Ghrd from the encoder 10 is not recorded.
In the recording and reproducing apparatus 14, the input signals Ghdr and Gsdh (or Gsd) are recorded on a video tape, etc., separately. In reproduction, the HD image signal is reproduced by adding the additional image signal Ghdr to the SD image signal Gsdh, and the SD image signal is reproduced by decoding only the SD image signal Gsdh (or Gsd).
As mentioned, the following advantages are obtained by separating the HD image signal Ghd into the SD image signal Gsdh and the additional image signal Ghdr:
(1) When a tape on which both the SD image signal Gsdh and the additional image signal Ghdr are recorded simultaneously is used, it is possible to reproduce either an HD image or an SD image. When a SD reproducing apparatus capable of reproducing only an SD signal is used, it is possible to reproduce the SD image. PA1 (2) The SD reproducing apparatus dedicated to reproducing the SD image signal can reproduce from a magnetic tape on which the SD image signal Gsd is recorded by means of the SD recording apparatus capable of recording a SD signal. Further, an apparatus capable of reproducing the HD image signal can reproduce such magnetic tape as the HD image by making the additional image signal Ghdr "O" or reproduce the SD image signal as the SD image. PA1 (3) Consequently, it is possible to construct a system in which the HD image and the SD image are compatible. PA1 (a) A position shift is performed by post-process of a current TV decoder. PA1 (b) Scan line position of HDTV is preliminarily shifted by a pre-process of a HDTV encoder and then returned by the post-process of a HDTV decoder. PA1 (c) Different QMF Quadrature Mirror filter filters (filters 16-18) are used for a first field and a second field.
When the HD and SD images have an interlace structure, there is a time difference between fields constituting a frame. When an image corresponding to the SD image is derived by vertically sampling an HD image from an HD frame in the ratio of 2:1 as shown in FIG. 2, only one field image of the HD image is sampled. Thus, any movement of an image corresponding to the sampled SD image will not be smooth. Therefore, deriving the image corresponding to the SD image should be performed after field separation of the HD image.
The High-Vision system, for example, is utilized for the HD image and the NTSC system is used for the SD image. In each of these systems, the 2:1 interlace structure is employed. Accordingly, in the description of the prior art shown below, the image signal corresponding to the SD image will be described as being derived after the HD image is field-separated.
The signal processing in the encoder 10 of FIG. 1 for separating the HD image signal into the SD corresponding image signal Gsdh and the additional image signal Ghdr is performed according to one of the following three methods: